US10181291B2 - Organic light emitting display device having compensation pixel structure - Google Patents
Organic light emitting display device having compensation pixel structure Download PDFInfo
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- US10181291B2 US10181291B2 US16/026,219 US201816026219A US10181291B2 US 10181291 B2 US10181291 B2 US 10181291B2 US 201816026219 A US201816026219 A US 201816026219A US 10181291 B2 US10181291 B2 US 10181291B2
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Definitions
- the present invention relates to an organic light-emitting display device.
- Organic light-emitting display devices that are recently in the spotlight as next generation display devices have advantages, such as relatively fast response speeds, high light emitting efficiency and luminance and wide viewing angles, since they use organic light-emitting diodes (OLEDs) that emit light by themselves.
- OLEDs organic light-emitting diodes
- Organic light-emitting display devices have a matrix structure in which pixels including organic light-emitting diodes are arranged, in which the brightness of each pixel selected by a scanning signal is controlled according to the grayscale of data.
- Each pixel in such an organic light-emitting display device includes an organic light-emitting diode (OLED) as well as a driving transistor for driving the OLED.
- the driving transistor has unique characteristics such as a threshold voltage and mobility. A difference in the characteristic value between the driving transistors of adjacent pixels may reduce the luminance quality of the corresponding pixels.
- Various aspects of the present invention provide an organic light-emitting display device having a pixel structure able to significantly improve threshold voltage compensation capability and range by compensating for a loss in a threshold voltage that would occur during operation.
- an organic light-emitting display device having a pixel structure able to compensate for mobility and control a mobility compensation time based on a capacitor design within the pixel structure, thereby achieving a sufficient data writing time.
- an organic light-emitting display device having a pixel structure that has superior global uniformity characteristics.
- an organic light-emitting display device that includes: a display panel on which data lines and gate lines are disposed to define a number of pixels; a data driver driving the data lines; a gate driver driving the gate lines; and a timing controller controlling the data driver and the gate driver.
- Each of the pixels includes: an organic light-emitting diode; a driving transistor driving the organic light-emitting diode, wherein the driving transistor includes a first node forming a gate node, a second node connected to the organic light-emitting diode and a third node connected to a driving voltage line; a first transistor controlled by a first scanning signal, the first transistor being connected between a source voltage line and the first node of the driving transistor; a first storage capacitor connected between the first node and the second node of the driving transistor; a second storage capacitor and a boost capacitor between the first node and the second node of the driving transistor; a second transistor controlled by a second scanning signal, the second transistor being connected between a hold node to which the second storage capacitor and the boost capacitor are connected and a corresponding data line of the data lines; and a third transistor controlled by a third scanning signal, the third transistor being connected between the first node of the driving transistor and the hold node.
- an organic light-emitting display device that includes: a display panel on which data lines and gate lines are disposed to define a number of pixels; a data driver driving the data lines; a gate driver driving the gate lines; and a timing controller controlling the data driver and the gate driver.
- Each of the pixels includes: an organic light-emitting diode; a driving transistor driving the organic light-emitting diode, wherein the driving transistor includes a first node forming a gate node, a second node connected to the organic light-emitting diode and a third node connected to a driving voltage line; a first transistor controlled by a first scanning signal, the first transistor being connected between a source voltage line and the first node of the driving transistor; a first storage capacitor connected between the first node and the second node of the driving transistor; a second storage capacitor and a boost capacitor between the first node and the second node of the driving transistor; a second transistor controlled by a second scanning signal, the second transistor being connected between a hold node to which the second storage capacitor and the boost capacitor are connected and a corresponding data line of the data lines; a third transistor controlled by a third scanning signal, the third transistor being connected between the first node of the driving transistor and the hold node; and a fourth transistor connected between the second node of the
- an organic light-emitting display device that includes: a display panel on which data lines and gate lines are disposed to define a number of pixels; a data driver driving the data lines; a gate driver driving the gate lines; and a timing controller controlling the data driver and the gate driver.
- Each of the number of pixels includes: an organic light-emitting diode; a driving transistor driving the organic light-emitting diode, wherein the driving transistor includes a first node forming a gate node, a second node connected to the organic light-emitting diode and a third node connected to a driving voltage line; a first transistor controlled by a first scanning signal, the first transistor being connected between a source voltage line and the first node of the driving transistor; a first storage capacitor connected between the first node and the second node of the driving transistor; a second storage capacitor and a boost capacitor between the first node and the second node of the driving transistor; and a second transistor controlled by a second scanning signal, the second transistor being connected between a hold node to which the second storage capacitor and the boost capacitor are connected and a corresponding data line of the data lines.
- an organic light-emitting display device that includes: a display panel on which data lines and gate lines are disposed to define a number of pixels; a data driver driving the data lines; a gate driver driving the gate lines; and a timing controller controlling the data driver and the gate driver.
- Each of the number of pixels includes: an organic light-emitting diode; a driving transistor driving the organic light-emitting diode, wherein the driving transistor includes a first node forming a gate node, a second node connected to the organic light-emitting diode and a third node connected to a driving voltage line; a first transistor controlled by a first scanning signal, the first transistor being connected between a source voltage line and the first node of the driving transistor; a first storage capacitor connected between the first node and the second node of the driving transistor; a second storage capacitor and a boost capacitor between the first node and the second node of the driving transistor; a second transistor controlled by a second scanning signal, the second transistor being connected between a hold node to which the second storage capacitor and the boost capacitor are connected and a corresponding data line of the data lines; and a third transistor connected between the second node of the driving transistor and an initialization voltage line, the third transistor being controlled by the second scanning signal by which the second transistor is controlled.
- the organic light-emitting display device has the pixel structure able to significantly improve threshold voltage compensation capability and range by compensating for a loss in a threshold voltage that would occur during operation.
- the organic light-emitting display device has the pixel structure able to compensate for mobility and control a mobility compensation time based on a capacitor design within the pixel structure, thereby achieving a sufficient data writing time.
- the organic light-emitting display device has the pixel structure having superior global uniformity characteristics.
- FIG. 1 is a schematic system configuration view illustrating an organic light-emitting display device according to exemplary embodiments of the present invention
- FIG. 2 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device according to a first exemplary embodiment of the present invention
- FIG. 3 is an operation timing diagram of a pixel having the pixel structure of the organic light-emitting display device according to the first exemplary embodiment
- FIG. 4 is a circuit diagram illustrating a parasitic capacitor component of the pixel structure of the organic light-emitting display device according to the first exemplary embodiment
- FIG. 5 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device according to a second exemplary embodiment of the present invention.
- FIG. 6 is an operation timing diagram of a pixel having the pixel structure of the organic light-emitting display device according to the second exemplary embodiment
- FIG. 7A , FIG. 7B , FIG. 8A , FIG. 8B , FIG. 9 , FIG. 10A , FIG. 10B , FIG. 11 , FIG. 12A and FIG. 12B are circuit diagrams illustrating the operation according to process steps and graphs illustrating voltage changes at major nodes in the pixel structure of the organic light-emitting display device according to the second exemplary embodiment;
- FIG. 13A , FIG. 13B , FIG. 14A , FIG. 14B , FIG. 15A , FIG. 15B and FIG. 16 are graphs illustrating a variety of simulations on the pixel structure of the organic light-emitting display device according to the second exemplary embodiment
- FIG. 17 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device according to a third exemplary embodiment of the present invention.
- FIG. 18 is an operation timing diagram of a pixel having the pixel structure of the organic light-emitting display device according to the third exemplary embodiment
- FIG. 19 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device according to a fourth exemplary embodiment of the present invention.
- FIG. 20 and FIG. 21 are an operation timing diagram and a voltage change graph at major nodes in the pixel structure of the organic light-emitting display device according to the fourth exemplary embodiment
- FIG. 22 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device according to a fifth exemplary embodiment of the present invention.
- FIG. 23 is an operation diagram of a pixel having the pixel structure of the organic light-emitting display device according to the fifth exemplary embodiment.
- FIG. 1 is a schematic system configuration view illustrating an organic light-emitting display device 100 according to exemplary embodiments of the present invention.
- the organic light-emitting display device 100 includes a display panel 110 on which a plurality of data lines DL 1 to DLm and a plurality of gate lines GL 1 to GLn are disposed such that a number of pixels P are defined, a data driver 120 for driving the data lines LD 1 to DLm, a gate driver 130 for driving the gate lines GL 1 to GLn, and a timing controller 140 for controlling the data driver 120 and the gate driver 130 .
- the data driver 120 may include a plurality of data driver integrated circuits (also referred to as source driver integrated circuits) that may be connected to the bonding pads of the display panel 110 by a tape automated bonding (TAB) method or a chip-on-glass (COG) method, may be directly formed on the display panel 110 by a gate-in-panel (GIP) method, or may be integrated on the display panel 110 .
- TAB tape automated bonding
- COG chip-on-glass
- GIP gate-in-panel
- the gate driver 130 may be positioned only at one side of the display panel 110 as illustrated in FIG. 1 or may be divided into two sections each of which is positioned on either side of the display panel 110 .
- the gate driver 130 can provide each of the pixels with one or more scanning signals according to several pixel structures, which will be described later.
- the gate driver 130 may include a plurality of gate driver integrated circuits that may be connected to the bonding pads of the display panel by a tape automated bonding (TAB) method or a chip-on-glass (COG) method, may be directly formed on the display panel 110 by a gate-in-panel (GIP) method, or may integrated on the display panel 110 .
- TAB tape automated bonding
- COG chip-on-glass
- GIP gate-in-panel
- the timing controller 140 controls the operation timing of the data driver 120 and the gate driver 130 , and outputs a variety of control signals for this purpose.
- Each of the pixels of the organic light-emitting display device 100 includes an organic light-emitting diode (OLED) and a circuit for driving the OLED.
- OLED organic light-emitting diode
- the circuit for driving the OLED includes a driving transistor for supplying a current to the OLED, a switching transistor for applying a data voltage to a gate node of the driving transistor, and a storage capacitor for maintaining a data voltage for the period of one frame.
- the circuit can further include at least one transistor for compensating for the threshold voltage Vth and the mobility of the driving transistor.
- the pixel structures may vary according to the numbers and the connecting structures of the transistors and the capacitors included in the circuit.
- a pixel structure including four transistors and one capacitor according to a first exemplary embodiment will be described with reference to FIG. 2 to FIG. 4 .
- FIG. 2 is an equivalent circuit diagram illustrating the pixel structure of an organic light-emitting display device 100 according to the first exemplary embodiment.
- each pixel of the organic light-emitting display device 100 has a pixel structure including an organic light-emitting diode (OLED), a first transistor T 1 connected between a driving voltage line DVL through which a driving voltage EVDD is supplied and the OLED, a second transistor T 2 connected between a data line DL and a gate node DTG of the first transistor T 1 , a third transistor T 3 connected between a source node DTS of the first transistor T 1 and an initialization voltage line IVL through which an initialization voltage Vini is supplied, a fourth transistor T 4 connected between a reference voltage line through which a reference voltage Vref is supplied and the gate node DTG of the first transistor T 1 , and a storage capacitor Cstg connected between the gate node DTG and the source node DTS of the first transistor T 1 .
- OLED organic light-emitting diode
- the first transistor T 1 is a driving transistor for driving the OLED.
- the four transistors T 1 to T 4 are illustrated as being an N type, this is merely an illustrative example, and the four transistors may be designed to be a P type.
- FIG. 3 is the operation timing diagram of a pixel having the pixel structure of the organic light-emitting display device according to the first exemplary embodiment.
- the pixel having the pixel structure of the organic light-emitting display device 100 carries out an operation, including an initialization step, a threshold voltage sensing step, a data writing and mobility compensation step and an emission step.
- the second transistor T 2 is turned off, and the fourth transistor T 4 and the third transistor T 3 are turned on, such that the gate node DTG and the source node DTS of the first transistor T 1 are respectively initialized with a reference voltage Vref and an initialization voltage Vini.
- the third transistor T 3 and the fourth transistor T 4 are turned off, and the second transistor T 2 is turned on, such that a data voltage Vdata is applied to (or written in) the gate node DTG of the first transistor T 1 .
- the first transistor T 1 is turned on, and the voltage at the source node DTS of the first transistor T 1 increases.
- the increase in the voltage at the source node DTS of the first transistor T 1 is proportional to the mobility of the first transistor T 1 .
- a voltage change ⁇ DTS 1 at the source node DTS when the mobility of the first transistor T 1 is ⁇ 1 is greater than a voltage change ⁇ DTS 2 at the source node DTS when the mobility of the first transistor T 1 is ⁇ 2 .
- the voltage difference Vgs 1 between the gate node DTG and the source node DTS when the mobility of the first transistor T 1 is ⁇ 1 is smaller than the voltage difference Vgs 2 between the gate node DTG and the source node DTS at the mobility of the first transistor T 1 is ⁇ 2 .
- the mobility of the first transistor T 1 can be sensed, and variations in the mobility can be compensated by negative feedback.
- the emission step all of the transistors T 2 to T 4 except for the first transistor T 1 serving as the driving transistor are turned off.
- the OLED starts emitting light while the voltage at the source node DTS of the first transistor T 1 increases such that the current of the first transistor T 1 is identical to that of the OLED.
- the voltage at the source node DTS of the first transistor T 1 is expressed without the threshold voltage, and the voltage of the gate node DTG of the first transistor T 1 is expressed including the threshold voltage.
- the first transistor T 1 can drive the OLED free from the influence of the threshold voltage.
- the pixel structure of the organic light-emitting display device 100 according to the first embodiment makes possible the threshold voltage sensing, the mobility compensation and the like that have been problematic in the related art.
- the threshold voltage Vth of the first transistor T 1 serving as the driving transistor is stored in the source node DTS of the first transistor T 1 .
- the threshold voltage Vth stored in the source node DTS of the first transistor T 1 in this fashion is transferred to the gate node DTG of the first transistor T 1 serving as the driving transistor at the emission step.
- storing the threshold voltage in the source node DTS of the first transistor T 1 indicates that the voltage at the source node DTS of the first transistor T 1 can be expressed by the threshold voltage.
- the transfer of the threshold voltage Vth stored in the source node DTS of the first transistor T 1 to the gate node DTG of the first transistor T 1 indicates that the threshold voltage included in a voltage formula of the source node DTS of the first transistor T 1 is included in a voltage formula of the gate node DTG of the first transistor T 1 .
- a parasitic capacitor Cpara formed at the gate node DTG of the first transistor T 1 serving as the driving transistor may cause a loss in the threshold voltage.
- the loss in the threshold voltage caused by the parasitic capacitor Cpara formed at the gate node DTG of the first transistor T 1 may create a relatively-large gate source voltage at a low grayscale that is controlled based on a small gate source voltage of the driving transistor T 1 , thereby leading to a severe non-uniform image quality at the threshold voltage.
- the compensation range for the threshold voltage may be significantly reduced, thereby lowering the yield of transistors.
- exemplary embodiments (second to fifth embodiments) of the pixel structure that can significantly improve threshold voltage compensation capability and range by compensating for a loss in a threshold voltage that would occur during operation, can compensate for mobility and control a mobility compensation time based on a capacitor design within the pixel structure, thereby achieving a sufficient data writing time, and has superior global uniformity characteristics.
- FIG. 5 is an equivalent circuit diagram illustrating the pixel structure of the organic light-emitting display device 100 according to the second exemplary embodiment of the present invention.
- each of pixels defined on the display plane 110 of the organic light-emitting display device 100 includes: an organic light-emitting diode (OLED); four transistors including a driving transistor DT, a first transistor T 1 , a second transistor T 2 and a third transistor T 3 ; and three capacitors including a first storage capacitor Cstg 1 , a second storage capacitors Cstg 2 and a boost capacitor Cboost.
- OLED organic light-emitting diode
- the driving transistor DT drives the OLED, and includes a first node N 1 forming a gate node, a second node N 2 connected to the OLED and a third node N 3 connected to a driving voltage line DVL through which a driving voltage EVDD is supplied.
- the first transistor T 1 is controlled by a first scanning signal SCAN 1 , and is connected between a source voltage line SVL and the first node N 1 of the driving transistor DT.
- the first storage capacitor Cstg 1 is connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second transistor T 2 is controlled by a second scanning signal SCAN 2 , and is connected between a hold node Nh to which the second storage capacitor Cstg 2 and the booster capacitor Cboost are connected and a data line DL.
- the third transistor T 3 is controlled by a third scanning signal SCAN 3 , and is connected between the first node N 1 of the driving transistor DT and the hold node Nh.
- a driving voltage VDD applied to the third node N 3 of the driving transistor DT through the driving voltage line DVL is an AC voltage, which is shifted by 1 H.
- the driving voltage VDD at a low level can be indicated by VDD( ⁇ ), and the driving voltage VDD at a high level can be indicated by VDD(+).
- the three capacitors have their own capacitances. Comparing the capacitances of the first storage capacitor Cstg, the boost capacitor Cboost and the second storage capacitor Cstg 2 , the capacitance of the second storage capacitor Cstg 2 is designed smallest. The capacitances of the first storage capacitor Cstg 1 and the boost capacitor Cboost are designed similar to each other.
- FIG. 6 is an operation timing diagram of a pixel having the pixel structure of the organic light-emitting display device 100 according to the second exemplary embodiment.
- the pixel having the pixel structure of the organic light-emitting display device 100 carries out an operation, including an initialization step, a threshold voltage sensing step, a data writing and mobility compensation step and an emission step.
- a low level driving voltage VDD( ⁇ ) is applied to the third node N 3 of the driving transistor DT, the first transistor T 1 and the third transistor T 3 are turned on by a first scanning signal SCAN 1 and a second scanning signal SCAN 2 that are high level scanning signals, and the second transistor T 2 is turned on by a second scanning signal SCAN 2 that is a low level scanning signal.
- the hold node Nh and the first node N 1 of the driving transistor DT are initialized using a source voltage Vss, and the second node N 2 of the driving transistor DT is initialized using the low level driving voltage VDD( ⁇ ).
- VSS indicates a source voltage
- VSDD( ⁇ ) indicates a low level driving voltage
- a high level driving voltage VDD(+) is applied to the third node N 3 of the driving transistor DT, the first transistor T 1 is maintained at the turned-on state by a high level first scanning signal SCAN 1 , the second transistor T 2 is turned off by a low level second voltage signal SCAN 2 , and the third transistor T 3 is turned off by a low level third scanning signal SCAN 3 .
- the first node N 1 of the driving transistor DT is maintained at the source voltage VSS.
- the voltage at the second node N 2 of the driving transistor DT increases from the initialized voltage VDD( ⁇ ).
- the voltage increases from VDD( ⁇ ) to VSS-Vth, which is less than the source voltage Vss, i.e. the voltage at the first node N 1 of the driving transistor DT, by the threshold voltage Vth.
- a voltage change at the second node N 2 of the driving transistor DT is VSS-Vth-VDD( ⁇ ).
- the voltage at the hold node Nh increases according to the voltage change VSS-Vth-VDD( ⁇ ) at the second node N 2 of the driving transistor DT and a first capacitance ratio A.
- the voltage at the hold node Nh increases by a value obtained by multiplying the voltage change VSS-Vth-VDD( ⁇ ) at the second node N 2 of the driving transistor DT with the first capacitance ratio A.
- the first capacitance ratio A is a value obtained by dividing the capacitance of the second storage capacitor Cstg 2 with a total of the capacitance of the boost capacitor Cboost and the capacitance of the second storage capacitor Cstg 2 .
- VSS indicates a source voltage
- Vth indicates a threshold voltage of the driving transistor DT
- VDD( ⁇ ) indicates a low level driving voltage
- A indicates a first capacitance ratio
- Cstg 2 indicates a capacitance of the second storage capacitor Cstg 2
- Cboost indicates a capacitance of the boost capacitor Cboost.
- the second transistor T 2 is turned on by a high level second scanning signal SCAN 2 , a data voltage Vdata is applied through the data line DL to the turn on second transistor T 2 , a high level driving voltage VDD(+) is applied to the third node N 3 of the driving transistor DT, and the first transistor T 1 is turned on by a low level first scanning signal SCAN 1 .
- the second transistor T 2 is turned on, by which the data voltage Vdata supplied through the data line DL is applied to the hold node Nh.
- a voltage change at the hold node Nh is expressed by Vdata ⁇ [VSS+A*(VSS ⁇ Vth ⁇ VDD( ⁇ ))].
- the voltage at the second node N 2 of the driving transistor DT increases further from the voltage VSS ⁇ Vth that has increased at the threshold voltage sensing step.
- a voltage change ⁇ Vu at the second node N 2 of the driving transistor DT due to this voltage increase may vary according to a voltage change ⁇ Vp at the hold node Nh.
- the voltage at the first node N 1 of the driving transistor DT increases from the source voltage VSS that has been maintained through the threshold voltage sensing step.
- the voltage at the first node N 1 of the driving transistor DT can increase according to the voltage change ⁇ Vp at the hold node Nh, the voltage change ⁇ Vu at the second node N 2 of the driving transistor DT in response to the mobility sensing operation, a second capacitance ratio B and a third capacitance ratio C.
- the voltage at the first node N 1 of the driving transistor DT increases further by a voltage value B* ⁇ Vp+C* ⁇ Vu, i.e. a total of a voltage obtained by multiplying the voltage change ⁇ Vp at the hold node Nh with the second capacitance ratio B and a voltage obtained by multiplying the voltage change ⁇ Vu at the second node N 2 of the driving transistor DT in response to the mobility sensing operation with the third capacitance ratio C.
- the second capacitance ratio B is a value obtained by dividing the capacitance of the boost capacitor Cboost with a total of the capacitance of the first storage capacitor Cstg 1 and the capacitance of the boost capacitor Cboost.
- the third capacitance ratio C is a value obtained by the capacitance of the first storage capacitor Cstg 1 with a total of the capacitance of the boost capacitor Cboost and the capacitance of the first storage capacitor Cstg 1 .
- This third capacitance ratio C can determine the rate at which the difference in the voltage between the first node N 1 and the second node N 2 of the driving transistor DT decreases.
- B C boost/( C stg1 +C boost)
- C C stg1/( C boost+ C stg1)
- VSS 0
- VSS indicates a source voltage
- Vth indicates a threshold voltage of the driving transistor DT
- VDD( ⁇ ) indicates a low level driving voltage
- Vdata indicates a data voltage
- ⁇ Vp indicates a voltage change at the hold node Nh
- ⁇ Vu indicates a voltage change at the second node N 2 of the driving transistor DT
- B indicates a second capacitance
- C indicates a third capacitance
- Cstg 1 indicates a capacitance of the first storage capacitor Cstg 1
- Cboost indicates a capacitance of the boost capacitor.
- Ids indicates a current flowing between the drain node N 3 and the source node N 1 of the driving transistor DT
- Vgs indicates a difference in the voltage between the first node N 1 and the second node N 2 of the driving transistor DT
- Vth is a threshold voltage of the driving transistor DT.
- k is a component about the mobility of the driving transistor DT, and is defined by mobility ⁇ , an oxide capacitance Cox, a channel width W and a channel length L.
- the current flowing between the drain node N 3 and the source node N 2 of the driving transistor DT is identical to a current Ioled flowing through the OLED.
- VSS indicates a source voltage
- Vth indicates a threshold voltage of the driving transistor DT
- VDD( ⁇ ) indicates a low level driving voltage
- Vdata indicates a data voltage
- ⁇ Vp indicates a voltage change at the hold node Nh
- ⁇ Vu indicates a voltage change at the second node N 2 of the driving transistor DT
- A indicates a first capacitance ratio
- B indicates a second capacitance ratio
- C indicates a third capacitance ratio
- Cstg 1 indicates a capacitance of the first storage capacitor Cstg 1
- Cboost indicates a capacitance of the boost capacitor Cboost
- Cstg 2 indicates a capacitance of the second storage capacitor Cstg 2 .
- B*A*Vth is a part that cancels a loss in the threshold voltage. If the capacitances of the three capacitors Cstg 1 , Cstg 2 and Cboost are determined such that B*A is very small, B*A*Vth in Vgs ⁇ Vth becomes a negligibly small value. It is possible to make a current flow through the OLED without a significant effect on the threshold voltage Vth of the driving transistor DT.
- the capacitance of the capacitor Cstg 2 makes it possible to determine the amount to control at compensation for the loss in the information about the threshold voltage caused by the parasitic capacitor Cpara of the first node N 1 of the driving transistor DT.
- ⁇ Vu*(1 ⁇ C) indicates a decrease in the voltage difference Vgs between the first node N 1 and the second node N 2 of the driving transistor DT at the mobility sensing step.
- the third capacitance ratio C can reduce the rate at which the voltage difference Vgs decreases. Specifically, the third capacitance ratio C determines the reduction rate of the voltage difference Vgs between the first node N 1 and the second node N 2 of the driving transistor DT.
- FIG. 13A , FIG. 13B , FIG. 14A , FIG. 14B , FIG. 15A , FIG. 15B and FIG. 16 are graphs illustrating a variety of simulations on the pixel structure of the organic light-emitting display device 100 according to the second exemplary embodiment.
- FIG. 13A and FIG. 13B illustrate the results of simulations on the threshold voltage compensation capability of the pixel structure according to the second embodiment, performed by changing the second capacitor Cstg 2 in order to compensate for a loss in the threshold voltage caused by the parasitic capacitor Cpara.
- the pixel structure has the capacitance value of the second capacitor Cstg 2 that has optimum performance at both a low gray level (63 Gray) and a high gray level (255 Gray).
- FIG. 14A and FIG. 14B illustrate the results of simulations on the complex compensation capability of the pixel structure according to the second embodiment when both the threshold voltage Vth and the mobility of the driving transistor DT deviate from a reference.
- FIG. 15A and FIG. 15B illustrate the global uniformity of the pixel structure according to the second embodiment at a low gray level (63 Gray) and a high gray level (255 Gray).
- the pixel structure according to the second embodiment has superior global uniformity at either the low gray level (63 Gray) or the high gray level (255 Gray).
- FIG. 16 illustrates variations in a current (Y axis) flowing through the OLED according to data voltages (X axis) in the pixel structure according to the second embodiment.
- steps 1.5, 1.0, 0.5 and 0 pF indicate the capacitances between a first electrode (e.g. an anode) of the OLED and the source voltage VSS.
- FIG. 17 is an equivalent circuit diagram illustrating a pixel structure of an organic light-emitting display device 100 according to a third exemplary embodiment of the present invention.
- each of pixels of the organic light-emitting display device 100 has a pixel structure including: an organic light-emitting diode (OLED); five transistors including a driving transistor DT, a first transistor T 1 , a second transistor T 2 , a third transistor T 3 and a fourth transistor T 4 ; and three capacitors including a first storage capacitor Cstg 1 , a second storage capacitor Cstg 2 and a boost capacitor Cboost.
- OLED organic light-emitting diode
- the driving transistor DT includes a first node N 1 forming a gate node, a second node N 2 connected to the OLED and a third node N 3 connected to a driving voltage line DVL through which a driving voltage VDD is supplied.
- the first transistor T 1 is controlled by a first scanning signal SCAN 1 , and is connected between a source voltage line SVL and the first node N 1 of the driving transistor DT.
- the first storage capacitor Cstg 1 is connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second transistor T 2 is controlled by a second scanning signal SCAN 2 , and is connected between a hold node Nh and a data line DL.
- the third transistor T 3 is controlled by a third scanning signal SCAN 3 , and is connected between the first node N 1 of the driving transistor DT and the hold node Nh.
- the fourth transistor T 4 is connected between the second node N 2 of the driving transistor DT and an initialization voltage line IVL through which an initialization voltage Vini is supplied.
- the fourth transistor T 4 is commonly controlled by the third scanning signal SCAN 3 by which the third transistor T 3 is controlled.
- the 5T3C pixel structure according to the third embodiment illustrated in FIG. 17 is substantially identical to the 4T3C pixel structure according to the second embodiment illustrated in FIG. 5 , except that the driving voltage VDD supplied through a driving voltage line DVL is a DC voltage, and that the fourth transistor T 4 is added.
- the second node N 2 of the driving transistor DT is initialized by an initialization voltage IVL supplied through the initialization voltage line IVL in the pixel structure according to the third embodiment illustrated in FIG. 17 , whereas the second node N 2 of the driving transistor DT is initialized by VDD( ⁇ ) in the 4T3C pixel structure according to the second embodiment illustrated in FIG. 5 .
- the operation system and operating characteristics of the 5T3C pixel structure according to the third embodiment illustrated in FIG. 17 are substantially identical to those of the 4T3C pixel structure according to the second embodiment illustrated in FIG. 5 , except for the initialization of the second node N 2 of the driving transistor DT.
- the operation timing of a pixel having the 5T3C pixel structure according to the third embodiment illustrated in FIG. 17 is identical to the operation timing of a pixel having the 4T3C pixel structure according to the second embodiment illustrated in FIG. 5 .
- the pixel having the 5T3C pixel structure according to the third embodiment also carries out an operation, including an initialization step, a threshold voltage sensing step, a data writing and mobility compensation step and an emission step, as in the second embodiment.
- the fourth transistor T 4 is added to initialize the second node N 2 of the driving transistor DT.
- the DC driving voltage VDD is applied to the third node N 3 of the driving transistor DT, the first transistor T 1 is turned on by a high level first scanning signal SCAN 1 , the third transistor T 3 and the fourth transistor T 4 are turned on by a high level third scanning signal, and the second transistor T 2 is turned on by a low level second scanning signal SCAN 2 .
- the hold node Nh and the first node N 1 of the driving transistor DT are initialized by a source voltage VSS supplied through the first transistor T 1
- the second node N 2 of the driving transistor DT is initialized by the initialization voltage Vini supplied through the fourth transistor T 4 .
- the 4T3C pixel structure according to the second embodiment and the 5T3C pixel structure including one more transistor (the fourth transistor T 4 ) according to the third embodiment were described hereinabove.
- FIG. 19 is an equivalent circuit diagram illustrating the pixel structure of an organic light-emitting display device 100 according to the fourth exemplary embodiment of the present invention.
- the organic light-emitting display device 100 includes a display panel 110 on which a plurality of data lines DL 1 to DLm and a plurality of gate lines GL 1 to GLn are disposed such that a number of pixels P are defined, a data driver 120 for driving the data lines LD 1 to DLm, a gate driver 130 for driving the gate lines GL 1 to GLn, and a timing controller 140 for controlling the data driver 120 and the gate driver 130 .
- each of a plurality of pixels of the organic light-emitting display device 100 according to the fourth embodiment has a 3T3C pixel structure including an organic light-emitting diode (OLED), a driving transistor DT, a first transistor T 1 , a second transistor T 2 , a first storage capacitor Cstg 1 , a second storage capacitor Cstg 2 and a boost capacitor Cboost.
- OLED organic light-emitting diode
- the driving transistor DT serves to drive the OLED, and includes a first node N 1 forming a gate node, a second node N 2 connected to the OLED and a third node N 3 connected to a driving voltage line DVL.
- the first transistor T 1 is controlled by a first scanning signal SCAN 1 , and is connected between a source voltage line SVL and the first node N 1 of the driving transistor DT.
- the first storage capacitor Cstg 1 is connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the connecting node between the second storage capacitor and the boost capacitor forms a hold node Nh.
- the second transistor T 2 is controlled by a second scanning signal SCAN 2 , and is connected between the hold node Nh to which the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected and a data line DL.
- an AC driving voltage VDD is supplied to the third node N 3 of the driving transistor DT through the driving voltage line DVL.
- FIG. 20 and FIG. 21 are an operation timing diagram and a voltage change graph at major nodes in the pixel structure of the organic light-emitting display device 100 according to the fourth exemplary embodiment.
- the operation of a pixel having the 3T3C pixel structure according to the fourth embodiment is identical to the operation of a pixel having the 4T3C pixel structure according to the second embodiment.
- the operation of the pixel having the 3T3C pixel structure according to the fourth embodiment includes an initialization step, a threshold voltage sensing step, a data writing and mobility compensation step and an emission step, like the operation of the pixel having the 4T3C pixel structure according to the second embodiment.
- the operation of the pixel having the 3T3C pixel structure according to the fourth embodiment differs from the operation of the pixel having the 4T3C pixel structure according to the second embodiment in that the hold node Nh is initialized by a data voltage supplied through the data line DL, since the transistor (T 3 in FIG. 5 ) for initializing the hold node Nh is not provided.
- input data voltages are divided into a low level initialization data voltage Vo and a high level data voltage Vdata, and the hold node Nh is initialized by the initialization data voltage Vo.
- the hold node Nh is initialized by a voltage applied through the data line DL.
- the voltage applied through the data line DL is a voltage in which the low level initialization data voltage Vo and the high level data voltage Vdata alternate with each other.
- the transistor (T 3 in FIG. 5 ) connected between the hold node Nh and the first node N 1 of the driving transistor DT, as well as a scanning signal for controlling the transistor (T 3 in FIG. 5 ), can be precluded.
- an initialization time may be insufficient when performing the initialization through the data line DL.
- the hold node Nh is initialized to be in the shape of teeth by the low level initialization data voltage Vo, as illustrated in FIG. 21 , according to the type of the data voltage Vdata+Vo and the type of the second scanning signal SCAN 2 .
- the other operation at the threshold voltage sensing step, the data writing and mobility compensation step and the emission step
- the timing thereof are identical to those of the pixel having the 4T3C pixel structure according to the second embodiment.
- voltage changes at the first node N 1 , the second node N 2 and the hold node Nh in the pixel having the 3T3C pixel structure according to the fourth embodiment illustrated in FIG. 21 are identical to voltage changes at the first node N 1 , the second node N 2 and the hold node Nh in the pixel having the 4T3C pixel structure according to the second embodiment illustrated in FIG. 11 , except for a voltage change at the hold node at the initialization step.
- FIG. 22 is an equivalent circuit diagram illustrating the pixel structure of an organic light-emitting display device 100 according to the fifth exemplary embodiment of the present invention.
- the pixel structure of each of a plurality of pixels of the organic light-emitting display device 100 according to the fifth embodiment is substantially identical to the 3T3C pixel structure according to the fourth embodiment illustrated in FIG. 19 , except that a DC driving voltage VDD is applied to a third node N 3 of a driving transistor DT and, for this, a third transistor T 3 connected between a second node N 2 of a driving transistor DT and an initialization voltage line IVL is added.
- the driving transistor DT drives an organic light-emitting diode (OLED), and includes a first node N 1 forming a gate node, a second node N 2 connected to the OLED and the third node N 3 connected to the driving voltage line DVL.
- the first transistor T 1 is controlled by a first scanning signal SCAN 1 , and is connected between a source voltage line SVL and the first node N 1 of the driving transistor DT.
- the first storage capacitor Cstg 1 is connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected between the first node N 1 and the second node N 2 of the driving transistor DT.
- the connecting node between the second storage capacitor and the boost capacitor forms a hold node Nh.
- the second transistor T 2 is controlled by a second scanning signal SCAN 2 , and is connected between the hold node Nh to which the second storage capacitor Cstg 2 and the boost capacitor Cboost are connected and a data line DL.
- each of the plurality of pixels of the organic light-emitting display device 100 according to the fifth embodiment illustrated in FIG. 22 forms a 5T3C pixel structure, since this pixel structure has one more transistor (i.e. the third transistor T 3 ) than the 4T3C pixel structure according to the fourth embodiment illustrated in FIG. 19 .
- the third transistor T 3 added to the 5T3C pixel structure according to the fifth embodiment is commonly controlled by the second scanning signal SCAN 2 by which the second transistor T 2 is controlled.
- the operation timing of the pixel having the 5T3C pixel structure according to the fifth embodiment is substantially identical to the operation timing of the pixel having the 4T3C pixel structure according to the fourth embodiment illustrated in FIG. 20 , except that a DC driving voltage VDD is supplied and, consequently, an initialization voltage Vini is applied to the second node N 2 of the driving transistor DT through the third transistor T 3 connected to the second node N 2 of the driving transistor DT.
- the organic light-emitting display device has the pixel structure able to significantly improve threshold voltage compensation capability and range by compensating for a loss in a threshold voltage that would occur during operation.
- the use of the pixel structure according to the certain embodiments of the present invention makes it possible to store a relative threshold voltage in addition to an absolute threshold voltage, thereby compensating for a loss in the threshold voltage.
- the organic light-emitting display device has the pixel structure able to compensate for mobility and control a mobility compensation time based on a capacitor design within the pixel structure, thereby achieving a sufficient data writing time.
- the use of the pixel structure according to the certain embodiments of the invention makes it possible to control a mobility sensing time to a desirable time using an internal capacitor, thereby achieving a sufficient data writing time.
- the organic light-emitting display device has the pixel structure having superior global uniformity characteristics.
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Abstract
Description
Voltage of EN1=VSS
Voltage of EN1=VSDD(−)
Voltage of ENh=
Voltage of EN1=VSS
Voltage of EN2=VSS−Vth
Voltage of EN2=VSS+A*(VSS−Vth−VDD(−)),
where A=Cstg2/(Cboost+Cstg2)
If VSS=0,
Voltage of EN1=0
Voltage of EN2=−Vth
Voltage of EN2=−A*(VDD(−)+Vth)
Voltage of EN1=VSS+B*ΔVp+C*ΔVu
Voltage of EN2=VSS−Vth+ΔVu
Voltage of ENh=Vdata−Vss+A*(VSS−Vth−VDD(−))+ΔVp
where B=Cboost/(Cstg1+Cboost)
C=Cstg1/(Cboost+Cstg1)
If VSS=0,
Voltage of EN1=B*ΔVp+C*ΔVu
Voltage of EN2=−Vth+ΔVu
Voltage of ENh=Vdata=−A*(VDD(−)+Vth)+
Ids=k(Vgs−Vth)2, where k=½μCoxW/L Formula 6
Vgs−Vth=BsΔVp+CsΔVu−(−Vth+ΔVu)−Vth
=B(Data+A(VDD(−)+Vth))+CsΔVu+Vth−ΔVu−Vth
=BsData+BsAsVDD(−)+BsAsVth−ΔVus(1−C),
where A=Cstg2/(Cboost+Cstg2)
B=(Cboost/Cstg1+Cboost)
C=Cstg1/(Cboost+Cstg1) Formula 7
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US20230012381A1 (en) * | 2021-07-08 | 2023-01-12 | Lg Display Co., Ltd. | Pixel Circuit and Display Device Including the Same |
US11978406B2 (en) | 2021-10-28 | 2024-05-07 | Lg Display Co., Ltd. | Display device |
US11990502B2 (en) | 2017-08-31 | 2024-05-21 | Semiconductor Energy Laboratory Co., Ltd. | Display device and electronic device |
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US20180330670A1 (en) | 2018-11-15 |
ES2647817T3 (en) | 2017-12-26 |
EP2884484B1 (en) | 2017-08-16 |
CN104715716B (en) | 2017-09-05 |
KR101702429B1 (en) | 2017-02-03 |
EP2884484A1 (en) | 2015-06-17 |
CN104715716A (en) | 2015-06-17 |
US10062330B2 (en) | 2018-08-28 |
US20150170569A1 (en) | 2015-06-18 |
KR20150069288A (en) | 2015-06-23 |
PL2884484T3 (en) | 2018-01-31 |
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